Various heat transfer recording methods have been known so far. Among these methods, dye diffusion transfer recording systems attract attention as a process that can produce a color hard copy having an image quality closest to that of silver halide photography. Moreover, this system has advantages over silver halide photography: it is a dry system, it enables direct visualization from digital data, it makes reproduction simple, and the like.
In the dye diffusion transfer recording systems, a colorant (hereinafter also referred to as “a dye” or “an ink”)-containing heat-sensitive transfer sheet (hereinafter also simply referred to as “an ink sheet”) and a heat-sensitive transfer image-receiving sheet (hereinafter also simply referred to as “an image-receiving sheet”) are superposed, and the ink sheet is heated using a thermal head with which heat generation can be controlled by electric signals. Thereby a colorant in the ink sheet is transferred to the image-receiving sheet to record image information. More specifically, a transferred color image with a continuous change in color shading can be obtained by recording three colors including cyan, magenta and yellow, in the manner of one over another.
Recently, in the field of the dye diffusion transfer recording system, a variety of printers capable of printing at higher speed than old type printers have been developed and are spreading in the market. For example, the Printer ASK 2000 (trade name, manufactured by FUJIFILM Corporation), whose printing time per sheet is as short as the degree of about 8 seconds, contributes to a short cut of customer's waiting time in a shop.
In the heat-sensitive transfer image-receiving sheet of this system, a receptor layer is disposed on a support, and further a heat insulation layer may be disposed between the receptor layer and the support. The receptor layer is disposed to take therein a dye transferred from an ink sheet, thereby coloring the receptor layer. By a heat insulating effect given to the heat insulation layer, heat applied from a thermal head is remained therein. Migration of the dye is accelerated by the heat insulation layer so that a transferred dye density can be enhanced.
For this reason, for example, hollow polymer particles are used in the heat insulation layer, and various kinds of solutions are proposed to effectively enhance both heat insulating effect and cushion property owing to the hollow polymer particles (see, e.g., JP-A-8-25813 (“JP-A” means unexamined published Japanese patent application), JP-A-11-321128, and JP-A-6-171240).
Beside, it is known that the ink sheet may have a heat-resistant lubricating layer on a surface of the support (so-called back surface) opposite to the side of the thermal transfer layer containing a dye, and an inorganic filler is incorporated in the heat-resistant lubricating layer (see, e.g., JP-A-8-90945).
However, it is not always possible to obtain high quality prints stably in a recent high-speed printing. Therefore, it has been desired to develop an image forming method suitable for the high-speed printing.